Throughout the mechanical art there are numerous instances where screw fasteners and the like are employed to secure parts together and where forces exerted onto and through the fasteners and their related parts must be limited or set at some predetermined values which require that predetermined torsional forces be applied onto and through the fasteners when they are tightened or made up. To the above end, the prior art has developed and provides various kinds and casses of wrenches which limit or indicate the torsional forces delivered onto and through the fasteners with which they are related to effect tightening and setting of the fasteners.
One special type or class of torque wrench provided by the prior art comprises a hydraulically operated mechanism which includes a drive shaft carrying a work or fastener engaging head, a crank or lever arm drivingly coupled with the shaft by means of a ratchet mechanism, a double acting hydraulic cylinder and ram unit connected with the crank and operated (reciprocally) to drive the shaft and tighten the fastener engaged by said head. In addition to the above, such wrenches include elongate frames or bodies which carry the shafts and cylinder and ram units and which serve as reaction parts or as part of reaction mechanisms which engage and/or stop with or against a stationary reactive structure relative to which the shafts turn and which counter the forces delivered to the fasteners.
The above noted type or class of torque wrench is most commonly used in situations where large fasteners must be turned or worked upon and where very high torsional forces are to be applied into and through the fasteners. Such wrenches are particularly useful in those situations where working clearances at and about the fasteners to be worked upon is so limited that those other types and classes of wrenches which include elongate manually engageable lever arms cannot be effectively or conveniently used.
In hydraulic torque wrenches of the class here concerned with, the amount of torque delivered to related fasteners is supposed to be directly proportional to the pressure on the hydraulic fluid delivered into the cylinder and ram units. Accordingly, by adjusting the pressure of the fluid delivered to those units, as by means of a motor driven hydraulic pump and related pressure regulating means, the torsional forces delivered to the fasteners can be adjusted, as desired or as circumstances require.
In all of the prior torque wrenches of which we are aware, the drive shafts are rotatably supported or carried by pairs of spaced bearings set in frame structures which carry the cylinder and ram units and serve as reaction parts. The ratchet mechanisms in those wrenches, between the drive shafts and cranks thereof, include ratchet wheels fixed to the drive shafts, between the noted bearings. The ratchet mechanisms include one or more spring loaded pawls pivotally carried by the cranks and engageable with the ratchet wheels. The cranks are simple elongate lever arms with outer ends with which the cylinder and ram units are connected and which have inner ends arranged between the noted bearings. The inner ends have large apertures through which the shafts extend and in which the ratchet wheels are freely arranged. The apertures in the cranks are provided with recesses in which the spring loaded pawls are arranged. The teeth of the ratchet wheels and the pawls are disposed so that when the cranks are turned in one "drive" direction, the pawls engage the teeth on the wheels and establish driving engagement between the cranks and wheels and are such that when the cranks are turned in the other "return" direction, the pawls disengage the ratchet teeth and allow for substantial free relative rotation between the crank and the wheel.
While the above ratchet mechanism is a simple straight-forward and apparently effective mechanism, it has proven to be wanting and the frequent source of malfunctioning of such wrenches. In the ratchet mechanism of most prior art wrenches, a single pawl is provided. In those prior art structures where the ratchet mechanisms include a plurality of pawls, the pawls are not arranged about the ratchet wheels in balanced relationship. As a result, when the cranks are turned in said driven direction and the pawls establish driving engagement with their related ratchet wheels, the pawls urge the cranks radially to one side and out of axial alignment with the ratchet wheels and/or urge the ratchet wheels and drive shafts out of axial alignment with the crank. The above noted displacement of parts often upsets the geometry of the wrenches to an extent that when high forces are transmitted in and through the wrenches, excessive and unacceptable error exists between the input and output thereof. Further, where high forces are encountered, and the wheels shift out of axial alignment with the cranks, the teeth of the wheels engage the surfaces of the apertures in the cranks with resulting abrading away of and deformation of the teeth and of the crank. Such abrading and deforming of parts inevitably results in serious adverse effects.
In addition to the above, misalignment of the wheel and shaft assemblies relative to the cranks results in altering the geometry of the wrenches so that the shafts are urged laterally from central alignment within the bearings and in such a manner that increased friction losses are encountered. Such friction losses are frequently substantial and such that the work output of such wrenches is not uniform, predictable or dependable. Evidence of the foregoing is the requirement and provision of anti-friction bearings for the shaft in certain of those hydraulic torque wrenches provided by the prior art and/or by the apparent rapid degradation of the shaft bearings in such wrenches.
In theory, if the geometry of such wrenches is stable, the point of reaction for the wrenches is fixed and the related axes of the crank, ratchet wheel and output shafts remain concentric, the bearings for the shaft are substantially unloaded during driving motion of the wrenches and the provision of anti-friction bearings or the like, for the shafts, is not required.